I'm posting to Drupal6 and Blogspot blogs successfully using MarsEdit. However I also have accounts on a couple Ning sites and want to post to Ning based blogs w/ MarsEdit. Ning announced last summer that they now support the metaweblog API and specifically named MarsEdit as an app that would work.
Today I tried - edited a blog post using MarsEdit, clicked the Send To Blog button, and it gave me an error saying the server sent a response "Please enter content".
I tried looking here and a couple other places. FWIW the text is set to UTF-8. The Ning site in question is operated by a Norwegian but that might not mean anything. I am a moderator on that site but my access to administrator panels is limited.
FWIW MarsEdit does see my list of postings on that blog.
I eventually thought "screw it" and made a posting using the Ning site. Copied the HTML text out of the MarsEdit editor, pasted it into the Ning edit box, and it posted right away. THEN I clicked refresh in MarsEdit, it showed the new posting. I double clicked that posting and it came up correctly in the MarsEdit editor. Then I made a simple change to the text and clicked the Send To Blog button. It posted, but then over on the Ning the content of the posting was completely gone.
This indicates that MarsEdit is doing something wrong with the content
API endpoint: http://electricaid.ning.com/profiles/blog/xmlrpc
Blog ID: 1
Under editing I haven't checked the "encode with HTML entities" checkbox